Because greenhouse gas concentrations in the earth's atmosphere continue to rise, the probability of significant climate change increases (IPCC, 2001a). There have been many studies concerning the effects of elevated CO2 concentrations on terrestrial ecosystems, and, to a lesser extent, the influence of higher temperatures. Another aspect of global change, declining biodiversity, is less well studied. This project investigates the single-factor and combined impact of elevated temperatures and diversity loss. Future carbon budgets will be the reflection of antagonisms and synergies between these 2 critical drivers of carbon sequestration, but studies of interactions are almost non-existent.
The study uses artificially assembled grassland model ecosystems. In twelve sunlit, climate-controlled chambers at the UIA campus (F.W.O. project), half of the model ecosystems are subjected to a temperature increase of 3°C. In each chamber, 24 plant communities are grown containing either 1, 3 or 9 grassland species. The design of the growth chambers is multi-factorial, and contains all combinations of temperature and diversity, in 6 replicates.
The study consists of 3 sections:
(i) Carbon flux measurements and study of storage and turnover of soil carbon:
CO2-flux measurements enable us to quantify inputs through photosynthesis and outputs through aboveground and belowground respiration. Because these fluxes cannot be measured continuously, they are recontructed from discrete measurements by interpolation, based on the relationships of the C-balance components with their dominant drivers (mainly radiation or temperature). To this end we use infrared gas analysis in dynamic closed systems.
Soil carbon storage and turnover are analysed by d13C measurements of CO2 produced in the soil. Because C3 plants are grown on C4 soils, it is possible to separate soil respiration into root and microbial respiration.
(ii) Ecophysiological measurements:
Ecophysiological parameters will change in response to the 3 conditions simulated in this project (temperature increase, biodiversity change, and both), which can provide explanations for observed shifts in the carbon balance. We study (among other things) how stomatal resistance, nutrient uptake and nutrient use efficiency, and canopy temperature react to the induced changes.
(iii) Study of phenology and competition:
Changes in phenology can also have a large impact on the carbon balance, and temperature is an important factor in determining both the beginning and the end of the growing season. We are therefore monitoring changes in both the length and the dynamics of the growing season under conditions of elevated temperatures (and declining plant diversity), both in individual species and species assemblages. We are furthermore investigating alterations in species composition and we attempt to identify the type of plant characteristics that are favoured by exposure to the various factors of global change. These findings are linked to any observed changes in carbon fluxes.